Solid State Physics (Ashcroft/Mermin)

1. The problem statement, all variables and given/known data
For the 1st problem, part (b) at the end of chapter 1, I am not certain what the question means. The question is " In the Drude model the probability of an electron suffering a collision in any infinitesimal interval dt is just [tex]\frac{dt}{\tau}[/tex].

Show that the probability that the time interval between two successive collisions of an electron falls in the range between t and t+dt is [tex]{\frac{dt}{\tau}[/tex]*[tex]e^{\frac{dt}{\tau}[/tex]

3. The attempt at a solution
Does the question mean that the two collisions occur in the time interval from t and t+dt
or that the first collision occurs from the time 0 to t and that the second collision occurs from the time t to t+dt?